Comprehensive management of dog faeces: Composting versus anaerobic digestion

The objective of this work was to study the possibilities to manage and recycle dog faeces (DF) using biological processes, using two approaches: composting (C) and anaerobic digestion (AD). Thus, different experiments have been carried out: i) two laboratory/pilot scale experiments (self-heating and composting tests) and one, on a commercial scale; ii) two AD experiments. In both approaches, municipal waste such as the organic fraction of municipal solid waste (OMSW) and urban pruning waste (GW) were used as co-substrates. The results obtained regarding the optimization of the composting process indicated that the best strategy was the use of a 1:2 ratio of DF, a 1:4 ratio of OMSW, and a 1:4 ratio of GW, according to the thermal parameters studied (temperature and cumulative quadratic exothermic index (EXI2)), and the quality of the compost obtained. A potentially limiting factor of the process was the high salinity of the DF waste. In addition, AD experiments were performed on DF, OMSW, and GW wastes in controlled anaerobic systems at a laboratory scale. In these experiments, the biogas production obtained was 229 mL biogas/g total solids for the DF residue, 248 mL biogas/g total solids for GW, and 263 mL biogas/g total solids for OMSW. The co-digestion yields a clear improvement in the efficiency of the process against the use of a single residue, increasing the production of biogas by up to 27% with respect to that of the DF waste alone during the first 25 days of AD. The results obtained with these procedures have shown the possibilities to add value to this waste in an urban context where the circular economy represents an increasingly favourable scenario, including the generation of fertilisers and/or energy at a local scale, provided that the collection of dog faeces is optimized.